1. Field of the Invention
The present invention relates to electrical connectors and in particular to an electrical connector filter assembly.
2. Description of the Related Art
It is known to provide filters in electrical connectors for the purpose of protecting sensitive electronic components from currents and voltages which develop in a transmission cable due to electromagnetic and radio frequency interference. It is further known to use capacitive or tuned pi circuits for the purpose of shunting the transients to ground without affecting the primary signal carried by the cable. Because such filter components generally require special handling, however, which greatly increases the cost of assembling the connectors, use of filter connectors has heretofore been restricted to specialized applications in which the need for filtering outweighs cost considerations. Nevertheless, electromagnetic and radio frequency fields are everywhere, and therefore virtually all applications involving cable connections between electronic devices could benefit from the addition of input filtering using filter connectors. For example, while filter connectors have been relatively widely employed in military aircraft, they have yet to gain widespread acceptance from commercial and civilian aircraft manufacturers due to the costs involved, even though commercial and civilian aircraft are subject to much of the same electrical interference fields as are military aircraft.
A main problem in assembling a filter connector lies in establishing electrical connections between the individual filter elements and the signal carrying connector contacts on the one hand, and between the filter elements and a common ground on the other. It is of course essential that all electrical connections be secure, with as low an impedance as possible, but it is also desirable for the connections to be releasable, permitting in situ testing and subsequent repair of the filter component without having to discard the entire connector prior to completion of the connector by potting.
This problem would not be difficult to overcome, except that the connectors in question have become extremely small, with contact densities on the order of 0.09". A typical connector having a diameter of approximately 1" may carry more than 50 feedthrough signal contacts, each contact requiring filtering. The problem of providing a filter for each contact is simplified somewhat by using monolithic filter elements, in which the filter elements are in the form of blocks of dielectric material with buried interleaved electrodes, but such filter elements are fragile, relatively expensive, and difficult to customize for specific applications. In addition, monolithic filter elements are subject to design problems involving cross-talk, hole-to-hole capacitance, ground resistance and control of the capacitance of non-filter holes. These problems arise because the live electrodes in each of the holes are separated from each other only by the dielectric material, and because each hole, whether filtered or not, is surrounded by the dielectric.
A variety of filter connector designs have been proposed which offer partial solutions to the above problems. These include the designs shown in U.S. Pat. Nos. 4,954,794, 4,950,185, 4,741,710, 4,768,977, 4,494,092, 4,458,220; 4,275,945; 4,083,022; 4,079,343; 3,790,858; 3,569,915; 3,825,874; and 3,538,464. As noted above, however, none of these numerous designs has resulted in mass acceptance of filter connectors in contexts other than a few limited applications. Each of the designs in the above-noted patents offers advantageous features, but none combines all of these features with a view to optimizing the simplicity and ease of assembly of a high density filter connector.